Rosamond Mallory is probably the daughter of Roger and Sarah. maybe? most likely?

 I believe my 4th GG Rosamond Mallory is the daughter of Roger Mallory and Sarah Smith and I'll tell you why... Rosa married Stephen Bourne and his sister Elizabeth Bourne married George H Mallory. Usually when two siblings marry people with the same surnames they are related. So I think Rosamond Mallory is probably George's sister... or at least a relative of his. If Rosa is the sister of George then her parents are the same as his. Roger Mallory iv and Sarah Smith. Prove me wrong.... you can't? neither can I. As Roger Mallory's family is definitely related, it is highly likely that Rosa is the daughter of Roger Mallory and Sarah Smith so although I cannot confirm these findings, I cannot deny them either.